Technical Field
The present disclosure relates to a spring assembly, particularly to a spring assembly for absorbing and attenuating torsional vibration and a damper mechanism.
Background Information
In vehicles, spring assemblies are installed in a damper mechanism for, e.g., a clutch disc assembly, a flywheel assembly, a lock-up clutch for a torque converter, etc., so as to absorb and attenuate torsional vibration. The spring assemblies are disposed to elastically couple an input-side rotary member and an output-side rotary member in a circumferential direction. When the input-side rotary member and the output-side rotary member are rotated relatively to each other, the spring assemblies are configured to be compressed therebetween in a rotational direction. Additionally, torsional vibration inputted into the input-side rotary member is absorbed and attenuated by using the spring assemblies described above and a friction resistance portion configured to generate friction resistance in the relative rotation.
As a type of spring assembly described above, there has been known a spring assembly using so-called “nested springs” composed of two coil springs with one being nested in the other (see Japan Laid-open Patent Application Publication No. 2004-183871). The spring assembly using the nested springs includes an outer coil spring and an inner coil spring disposed in the interior of the outer coil spring. When both coil springs are compressed, this spring assembly exerts higher stiffness and generates larger load than a type of spring assembly using a single coil spring.
Japan Laid-open Patent Application Publication No. 2004-183871 describes that in each spring assembly using the nested springs, the free length of the inner coil spring is set to be shorter than that of the outer coil spring, whereby the inner coil spring is movable in a rotational direction in the interior of the outer coil spring.
In this construction, when compressed by torsional vibration, the inner coil spring is moved to the outer peripheral side by a centrifugal force, and slides against the inner peripheral surface of the outer coil spring. At this time, the inner peripheral surface of the outer coil spring is inevitably abraded by the sliding of the inner coil spring. Additionally, when both ends of the inner coil spring get stuck between windings of the outer coil spring by the sliding of the inner coil spring, chances are that flashes are formed at three consecutive windings including the endmost winding on each of the ends of the inner coil spring due to friction with the windings of the outer coil spring, and intrude as foreign objects into the slide part between the inner coil spring and the outer coil spring and so forth.